1. Field of the Invention
The present invention relates to a remote meter reading system for a meter, and more particularly, to an apparatus for counting the rotation frequency of a numeral wheel of a meter which counts the rotation times of the numeral wheel of a predetermined digit in existing meters by a light sensing method, so that the used amount of a supply such as gas can be monitored from a remote place.
2. Description of the Prior Art
The amount of usage of supplies, such as electricity, gas, or water, is metered when the supplies pass through a meter. The amount of usage is expressed by a number value of a numeral wheel counter disposed on the front side of a meter. The charge for supply usage is determined with respect to the amount of usage. A manual meter reading method, by which in order to read a meter for the amount of the supply used, a meter-reading person visits each consumer's house and reads a meter, needs a lot of time and efforts and also causes much inconvenience.
In order to solve the problems of this manual meter reading method, a system enabling remote automatic meter reading of a meter is strongly demanded. Among remote automatic meter reading systems of a meter there is a digital meter. This is a meter formed for a digital method, not for a mechanical method, and outputs the amount of the supply used as a digital electric signal such that a remote automatic meter reading system can be easily built. However, since this needs to replace existing mechanical type meters, the expense is high, and the economic efficiency is low. Accordingly, it is difficult to practically apply this to ordinary household use. Alternatively, there is a meter which embeds a magnetic type lead switch or a hole sensor in a mechanical meter and produces electric pulses as a means to count the rotation frequency of a numeral wheel of a meter. However, the meter also has the problem that an existing mechanical meter cannot be used as is, and it is highly probable that a metering error by a magnet occurs. Due to these problems, a light sensing type apparatus for counting the rotation frequency of a numeral wheel of a meter is greatly attracting attention because it can utilize an existing meter while minimizing the effect to the performance of a meter or safety.
As prior art related to an apparatus for counting the rotation frequency of a numeral wheel of a meter using a light sensing method, there are Korean Patent Registration No. 10-0287540 entitled “Apparatus for generating signal of usage amount of meter by light sensing”, Korean Patent Application Laid-open No. 2000-0066245 entitled “Apparatus for counting rotation frequency of numeral wheel of meter”, and Korean Utility Model Registration No. 20-0273026 entitled “Apparatus for counting rotation frequency of numeral wheel of meter”. In constructing an apparatus for counting the rotation frequency of a numeral wheel of a meter in a light sensing method, forming a light sensor by means of an infrared ray emitter and an infrared ray sensor is the most practical and competitive way, considering requirements such as economic efficiency, stability of operations, the life span, and low power consumption.
FIGS. 1a and 1b show the structure of an apparatus disclosed in the Korean Utility Model Registration No. 20-0273026. According to this apparatus, a reflection sheet 20 is attached to the outer surface of a predetermined numeral wheel 11a of a meter 5. In addition, an optical sensor unit 22 is formed with a light emitter 22a emitting light to the numeral wheel 11a and an optical sensor 22b detecting the light reflected by the reflection sheet and outputting the detected light as an electric signal. This optical sensor unit 22 is mounted on the inner surface of a housing 21 and then this housing 21 is detachably coupled with the cover 12 on the front of the meter 5 by covering the cover 12. The optical sensor unit 22 is formed by means of an infrared ray emitter 22a and an infrared ray sensor 22b. The optical sensor unit 22 and the reflection sheet 20 are installed only over the lowest digit numeral wheel. A part of the housing 21 on which the optical sensor unit 22 is mounted should be made to be opaque or translucent, while a part of the housing facing the numeral wheel counter formed with the remaining numeral wheels and a metal plat on the front of the meter, on which meter product information (the proper number of the meter, class, maximum usage amount per hour, maximum use pressure, an authentication institute, authentication number, etc.) is written, should be transparent. This is to enable a consumer or a meter reading person to read with the naked eye, to confirm that the amount of use measured by remote automatic meter reading matches the amount of use measured by manual meter reading, and also to confirm meter product information such as the proper number of the meter, the class of the meter, maximum allowable quantity of use per hour.
To the infrared ray emitter 22a, driving pulses as shown in FIG. 2a are provided as power such that infrared ray emission is intermittently repeated during the time when the driving pulses are provided. If the consumer uses a supply, for example, gas, the predetermined numeral wheel 11a to which the reflection sheet 20 is attached begins to rotate. If the reflection sheet 20 rotating together with the predetermined numeral wheel 11a comes just below the optical sensor unit 22 of the meter 5, an infrared ray emitted from the infrared ray emitter 22a is reflected by the reflection sheet 20 to the light sensor 22b. If the remaining section of the numeral wheel 11a on which the reflection sheet 20 is not attached comes below the light sensor 22, the reflection as such hardly occurs. As the predetermined numeral wheel 11a rotates, the section on which the reflection sheet 20 is attached and the remaining section on which the reflection sheet 20 is not attached pass alternately below the light sensor 22. As a result, a sensing signal obtained from the light sensor 22b has a shape in which there are pulses in a predetermined section, that is, in a reflection section, while there are no pulses in a predetermined section after a predetermined point, that is, in a non-reflection section, as shown in FIG. 2b. A means capable of counting pulses is connected to the output terminal of the light sensor 22b and by counting the frequency of repetition of the reflection section and non-reflection section, calculates the rotation frequency of the predetermined numeral wheel 11a. 
However, a meter may be installed outdoors or indoors and there is natural light or artificial light where the meter is installed. Generally, this external light includes an infrared ray having a wavelength that can be detected by the light sensor 22b. If the housing 21 is constructed as described above, though external light would not be incident directly on the light sensor 22b, external light penetrates into the transparent part on the front side of the housing 21c and is incident indirectly on the light sensor 22b, through complex multiple reflections between the numeral wheel counter, an inner surface of the housing 21c and the front surface part of the meter on which meter product information is written, and along the narrow space of the numeral wheels 11b on which the optical sensor unit 22 is not disposed, as shown in FIG. 1b. In other words, external light is incident on the numeral wheels 11b on which the optical sensor unit 22 is not disposed (particularly on the numeral wheels neighboring the numeral wheel 11a on which the optical sensor unit 22 is disposed), and diffusedly reflected by the numeral wheels. Part of the reflected light is incident on the numeral wheel 11a and is reflected by it to be mixed with the infrared ray emitted by the infrared ray emitter 22b, and is ultimately incident on the light sensor 22b, too. Particularly, since the front surface part of the meter on which meter product information is written is usually made of a metal plate with a very high reflection rate, for example, an aluminum plate 14, a considerable portion of external natural light or artificial light, which is incident on this part at a low angle, is strongly introduced into to the light sensor part. When this external light is introduced and mixed, the level of the output sensing signal from the light sensor 22b is raised both in the reflection section and the non-reflection section and the amplitude difference between the two sections is relatively reduced such that discrimination between the reflection section and the non-reflection section becomes difficult, as shown in FIG. 2c. Particularly, when the meter 5 is installed outdoors and exposed to sunlight, the strength of an external infrared ray which is mixed with the infrared ray originated from the light sensor 22b becomes very high. In this case, it is very difficult to distinguish the reflection section from the non-reflection section, which may result in a great deal of error in automatic meter reading.
As an alternative method to reduce this error, it can be considered to further raise the amplitude of a driving pulse of the light emitter 22a with taking the maximum level of an expected noise signal into consideration. However, this method increases power consumption and reduces a replacement cycle for battery which is used as a power source. Accordingly, it is difficult to employ this method. In addition, since there is a limit to the increase of the amplitude of the driving pulse of the light emitter 22a due to the intrinsic characteristic of the device, the amplitude increase should be limited under a predetermined value, which makes it difficult to solve the problem.
Meanwhile, in addition to the apparatus for counting the rotation frequency of a numeral wheel of a meter as described above, the entire optical remote meter reading system further comprises a pulse generator 30 which provides a driving pulse signal (Pin) to the light emitter 22a; an amplifier 32 which amplifies the output signal of the light sensor 22b; a micom 34 which by recognizing changes of ‘non-reflection→reflection→non-reflection’ through comparison of levels of the output pulses (Pout) from the light emitter 22b, counts the rotation frequency of the numeral wheel 11a; a transmitter 36 which wirelessly transmits usage amount data counted by the micom 34 together with consumer information; and a battery 38 which provides needed power to these elements.
Using commercial electric power source instead of a battery is not appropriate because the commercial electric power cannot be used as is due to a lot of noise. In addition, it imposes an additional burden on consumers and additional cabling works for power supply are needed. Accordingly, it is practically difficult to employ the method. There may be a compulsory examination for the effective period of a meter in each country. In Republic of Korea's case, the examination period for effective period of a meter is 5 years. The life span of a battery needs to be longer than this period. Accordingly, a remote meter reading system needs to be designed as an optimized energy saving type one which can minimize power consumption in operation. However, the prior art technologies described above only mention that a pulse signal is used as a driving signal, but fail to suggest a specific solution required for the energy saving design.